the Titans

In Greek mythology, the Titans , were a race of powerful deities that ruled during the legendary Golden Age. Their role as Elder Gods was overthrown by a race of younger gods, the Olympians, which effected a mythological paradigm shift that the Greeks may have borrowed from the Ancient Near East.
The Twelve
There are twelve Titans from their first literary appearance, in Hesiod, Theogony; Pseudo-Apollodorus, in Bibliotheke, adds a thirteenth Titan Dione, a double of Theia; both names simply signify "the Goddess". In Greek the six male Titans are the Titanes, and the females are the Titanides ("Titanesses"). Most of the Titans were associated with various primal concepts, some of which are simply extrapolated from their names: ocean and fruitful earth, sun and moon, memory and natural law. The twelve first-generation Titans were ruled by the youngest, Cronus (Roman Saturn), who overthrew their father, Ouranos ('Sky' or 'Heaven'), at the urgings of their mother, Gaia ('Earth').

Several Titans produced offspring who are also known as "Titans." These second-generation Titans include the children of Hyperion (Helios, Eos, and Selene), the daughters of Coeus (Leto and Asteria), and the sons of Iapetus (Prometheus, Epimetheus, Atlas, and Menoetius).

The Titans preceded the Twelve Olympians, who, led by Zeus, eventually overthrew them in the Titanomachy ('War of the Titans'), a second shift in the power structure of the gods. The Titans were then imprisoned in Tartarus, the deepest part of the underworld, with a few exceptions, explained by there having been those who did not fight against Zeus
In Hesiod
In Hesiod's Theogony the twelve Titans precede the Hecatonchires (the "Hundred-handers") and Cyclopes as the oldest set of children of Uranus, and Gaia:

"Afterwards she lay with Uranus and bore deep-swirling Oceanus, Coeus and Crius and Hyperion and Iapetus, Theia and Rhea, Themis and Mnemosyne and gold-crowned Phoebe and lovely Tethys. After them was born Cronus the wily, youngest and most terrible of her children, and he hated his lusty sire."
Uranus kept all of Gaia's children trapped within her womb, and Gaia groaned from the strain. Eventually, Cronus (Kronos), her youngest child at the time, volunteered to set upon his father, castrating him with a sickle she provided him, thereby freeing Gaia's children and setting himself up as king of the titans with Rhea as his wife and queen.

Rhea gave birth to a new generation of gods fathered by Cronus, but, in fear that they too would eventually overthrow him in turn, he swallowed them whole one by one; Hades he flung into Tartarus, Poseidon into the sea.[3] Only Zeus was saved: Rhea gave Cronus a stone in swaddling clothes in his place, and placed the infant Zeus in Crete[4] to be guarded by the Kouretes. Hyginus' version of the myth of Zeus raised by the nymph Amalthea, has her hiding the infant Zeus by dangling him by a rope from a tree so that he was suspended, neither on the earth, in the sea, or in the sky,[5] all of which were ruled by his father, Cronus. Still other versions of the tale say that Zeus was raised by his grandmother, Gaia.

Once Zeus reached adulthood, he subdued Cronus by wile rather than force, using a potion concocted with the help of Metis, goddess of prudence, to force Cronus to vomit up Zeus's siblings. A war between younger and older gods commenced, in which Zeus was aided by the Hecatonchires and Cyclopes, who had once again been freed from Tartarus. Zeus won after a long struggle, and cast many of the Titans down into Tartarus.

Yet the older gods left their mark on the world: Oceanus continued to encircle the world, and the name of "bright shining" Phoebe was attached as an epithet to effulgent Apollo, "Phoebus Apollo". The epithet was also associated with his sister, Artemis, who has also been called Phoebe. Some of the Titans, it was affirmed, had not fought the Olympians, which justified their roles as key players in the new administration: Mnemosyne as a Muse, Rhea, Hyperion, Themis, or the "right ordering" of things and Metis.